Drill King International is exploring reverse-circulation drilling opportunities in Chile

The new XT RC50 hammer from Drill King International completed drilling trials at the beginning of August 2016. This 5in (127mm) reverse-circulation (RC) hammer is the first one from the XT (Extreme Torque) series, introduced by the down-the-hole (DTH) drilling equipment manufacturer from Texas, US. The XT RC hammer series will complement Drill King's extensive line of DTH air- and water-powered hammers.

As with conventional DTH air hammers, the compressed air powers the RC hammer and carries the cuttings out of the hole. In RC drilling though, the cuttings are channelled back to the surface through the inner tubes in the RC hammer and, consequently, the drill rod, rotational head and sample hose, which is attached to the top of the 'cyclone', where the cuttings are slowed down, separated from the air and collected in a samples bag.

The need for clean, uncontaminated samples led to the development of the RC hammers in the 1990s, and RC drilling technology has been continually improving ever since to address the demand for drilling deeper and in more difficult geological conditions.

This constantly growing demand for RC drilling presented Drill King International with an opportunity to develop its own RC hammer line and thus, complement the RC bits product line, which was already manufactured for other RC hammer brands.

The XT RC50 hammer was conceived at the start of 2016 with the goal of creating a simpler design with fewer internal parts that would last longer. The inner sampling tube, which provides a continuous sealed pathway for the drill cuttings from the bit face to the surface, was given particular engineering attention as it is a critical component that normally wears prematurely. For this reason, Drill King fine-tuned its steel material selection and heat-treating specifications to produce a sampling tube with wear resistance properties. The XT RC50 is easy to disassemble and put back together as it features only 11 internal parts (not counting the o-ring seals). All hammer parts are precisely machined to eliminate air leakage, boosting drilling penetration rates and optimising air consumption.

Put To The Test

The XT RC50 hammer design was conceived and developed in partnership with Drill King International's distributor for Chile, Argentina and Peru, Drillers Supply, which administered the drilling trials on two different job sites, run by independent drilling contractors. Both trials were at copper greenfield exploration sites, located approximately 200km away from the Drillers Supply headquarters in Antofagasta, Chile, at altitudes of 1,200-1,500m above sea level.

The first trial began on July 30 at 1,500m above sea level in the middle of the desert, 230km from Antofagasta. The XT RC50 hammer started drilling at a depth of 130m and performed flawlessly until the 310th metre when the drilling was interrupted due to an issue with the drilling rig.

This was quite unexpected as the rig was only a year old and the air compressor was rated at 350psi/1,350CFM. Yet, it has to be noted that the site conditions are quite uncommon with the first 140-200m consisting of overburden. The initial overburden is drilled with RC tricone and RC bit sub for recovery of samples. Past the overburden, 53A\n (146mm) or a smaller RC bit is used for drilling holes up to 600-700m depths.

For this particular trial, the RC bit from Drill King was in the 55/ein (143mm) size and was equipped with the Dyanite grade of carbide buttons, which are well suited for the abrasive and fractured formation encountered for at least 20% of the hole drilled.

The second trial took place 200km from Antofagasta at 1,200m above sea level on August 8-9. The XT RC50 hammer started drilling at 28m until it reached 260m. Then, the RC bit was re-sharpened with a CME grinder. Afterwards, drilling continued up to 388m, meaning that the hammer and bit drilled 360m within two days or four drilling shifts. In this particular hole, 120m were fractured ground and gravel and the remaining 168m were rock. After completing the hole, the drilling contractor pulled the hammer out to change the inner tube, which lasted 360m as well.

Overall, both drilling contractors were satisfied with the performance of the XT RC50 hammer. They highlighted the simplicity of its design as the main advantage, as Drill King's RC hammer does feature fewer parts than other products, which is an improvement for RC drillers.

Drill King International is already looking into developing other RC hammer sizes. Yet, for the short term, the Texan manufacturer offers RC conversion kits, which allow the use of conventional DTH air hammers for RC drilling. The demand for RC drilling equipment is only expected to grow in the future as RC drilling remains the most cost-efficient and accurate method for initial exploration, orebody development and pit grade-control drilling.

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